Transformer structure and method of making the same



June 3, 1969 F. M. MINKS 3,448,423

TRANSFORMER STRUCTURE AND METHOD OF MAKING THE SAME Original Filed March ll, 1966 Q i w I --..=-a;"! llillllllllli '2!!! :t? i V f /I a //-"1\ A INVENTOR 0Y0 M MAI/(S BY United States Patent 0 US. Cl. 336-96 6 Claims ABSTRACT OF THE DISCLOSURE A transformer includes a primary winding wound as a frustoconical-shaped spirally wound coil preferably hav ing inner and outer turns corresponding to the inner and outer diameters of the secondary winding. The secondary winding is an annular or doughnut-shaped member and includes a wire conductor wound on a central insulating tube as a spiral multilayer coil with insulation layers interposed between each turn of the secondary winding. The primary winding is disposed to one side of the secondary coil in coaxial alignment therewith and with the low voltage ends of the primary and the secondary windings in axially aligned relationship. The high voltage turn of the primary is therefore spaced axially from the high voltage turn or turns of the secondary. The spiral primary winding and the secondary winding are potted within an insulating material such as a suitable plastic with the high voltage lead of the secondary projecting outwardly from the periphery of the secondary coil and the leads of the primary winding projecting laterally from the side of the plastic shell.

This is a continuation of application Ser. No. 533,542, now abandoned, filed Mar. 11, 1966.

This invention relates to a transformer structure and to the method of making the same and particularly to a transformer structure having a primary winding close coupled to a secondary Winding with optimum distribution of insulation between the primary and the secondary.

Transformer structures may be employed to increase a low voltage to a relatively high voltage. For example. ignition systems for automobiles, outboard motors and other internal-combustion engines have for many years employed a low voltage pulse through a primary winding to store energy in a core and induce a high voltage pulse in a secondary winding upon opening of the primary circuit. The secondary winding is connected to the spark plugs or other firing systems. In such systems, fast rise of a high voltage pulse is desirable and a highly satisfactory induction coil or transformer unit is shown and described in applicants copending application, entitled High Voltage Transformer, which was filed on Apr. 30, 1965, with Ser. No. 452,323, now abandoned, and is assigned to the same assignee as the present application. That application particularly discloses a highly improved secondary winding for high voltage transformers particularly adapted for ignition systems and the like. The primary winding is shown as a generally pancake coil formed from a spirally wound, fiat conductor and disposed immediately adjacent to the one side of the annular shaped secondary for maximum coupling.

The present invention is directed to a very simple and practical means of forming the primary winding for establishing optimum electrical insulating characteristics with respect to a secondary and to a practical method of assembling the primary and the secondary.

Generally, in accordance with the present invention, the secondary winding is wound as an annular or doughnut shaped member; preferably in accordance with the teaching of the previously identified copending application. The primary winding is wound as a frustoconical-shaped spirally wound coil preferably having inner and outer turns corresponding to the inner and outer diameters of the secondary winding. The primary winding is disposed to one side of the secondary coil in coaxial alignment therewith the low voltage ends of the primary and the secondary windings in axially aligned relationship. The high voltage turn of the primary is therefore spaced axially from the high voltage turn or turns of the secondary. The spiral primary winding and the secondary winding are potted within an insulating material such as a suitable plastic with the high voltage lead of the secondary projecting outwardly from the periphery of the secondary coil and the leads of the primary winding projecting latterally from the side of the plastic shell.

The unit is preferably constructed in a novel manner, as follows. The primary coil is wound as a spiral having the axial lead of each convolution greater than the final length in the assembled transformer. The secondary coil is mounted Within a mold with suitable means for holding the coil with the outer peripheral surfaces spaced from the surfaces of the mold to permit essentially complete encapsulation of the secondary. The frustoconically-shaped primary winding is disposed within the mold assembly which is then closed to compress the primary winding against the side of the secondary Winding whereby the primary winding functions as a spring to properly hold and locate the secondary coil while spacing the several turns of the primary winding in the desired relationship with respect to the secondary winding. In a preferred construction, the secondary winding is assembled with a fiber or other insulating inner tube which projects axially from one end. A fiber washer or the like is disposed over the adjacent planar ends of the tube and the secondary winding and the inner turn of the primary winding is connected to the inner turn of the secondary winding. The secondary winding and the tube with the primary winding are slid over a center post in one part of a two piece mold with the fiber tube resting on the base of the mold to hold the secondary coil in spaced relation to the base of the mold. The second part of the mold is then assembled and compresses the primary coil spring to hold the secondary winding and the primary winding in proper rela tionship Within the mold. The mold is then filled with a suitable plastic and after the plastic has set sufficiently, the mold is separated and the complete assembly is removed.

The present invention provides an improved transformer arrangement and an improved method of making such a transformer.

The drawing furnished herewith illustrates a preferred construction of the present invention in which the above advantages and features are clearly disclosed as well as others which will be clear from the following description to those skilled in the art.

In the drawing:

FIG. 1 is a perspective view of a finished transformer constructed in accordance with the present invention;

FIG. 2 is a vertical cross section through the transformer shown in FIG. 1;

FIG. 3 is an enlarged fragmentary view showing the primary to secondary low voltage connection;

FIG. 4 is an enlarged fragmentary view showing the secondary high voltage connection; and

FIG. 5 is a diagrammatic view showing the mold and method of assembly.

Referring to the drawings and particularly to FIG. 1, a finished potted transformer unit is illustrated of a construction suitable as an induction coil or transformer of a capacitor discharge ignition system wherein the transformer unit is connected between the capacitor and the firing means, not shown. The illustrated unit includes a generally rectangular body 1 formed of a suitable potting material or plastic and having a central opening to accommodate a core structure 2, shown in phantom. A pair of primary leads 3 projects from the side of the rectangular body 1 generally in radial alignment from the center of the core opening. A tubular secondary lead socket 4 projects centrally from one side of the periphery of body 1 to receive an ignition coil lead 5 which in an ignition system is connected to a distributor, not shown, in accordance with the usual connection. The body 1 is formed with corner mounting notches 6 to receive clamping bolts, not shown for securing the core structure 2 in place and to provide a mounting means, if desired.

Referring particularly to the cross sectional view of FIG. 2, a secondary winding 7 is shown as an annular or doughnut-shaped member mounted concentrically within the plastic body 1. The secondary winding 7 is formed generally in accordance with applicants previously referred to copending application and as most clearly appears in the fragmentary views of FIGS. 3 and 4 includes a wire conductor 8 wound as a spiral multilayer coil with insulation layers 9 interposed between each turn of the secondary winding. The secondary winding 7 is wound on a small fiber or plastic tube 10 which has an axial length corresponding to that of the secondary. An assembly tube 11 of plastic or the like is suitably secured within tube 10 with one end coplanar with tube 10 and the face of winding 7 and the opposite end projecting axially outwardly to the outer plane of body 4.

In practice, a plurality of secondary windings may be wound on an elongated tubular fiber tube which is then severed to form the individual units secured to the assembly tube 11, as shown in FIG. 2. This is a known convenient and practical method of manufacturing secondary windings for commercial application.

As most clearly shown in FIGS. 2 and 4, the outer end of the secondary winding 7 is secured in a conventional manner to the inner surface of a small conductive strip 12 which overlies the outer surface of the coil and is secured thereto as by solder 13 or other suitable means, not shown. The socket 4 and the strip 12 are in alignment and a tubular metallic contact member 14 is soldered or otherwise secured to the outer surface of the strip 12 and lines the inner surface of the socket 4. The contact member 14 includes a circumferential locking recess 15 to mate with a correspondingly formed contact portion on the end of the coil lead 5.

The inner end of the secondary winding 7 is connected by a small connecting lead 16 to an inner turn of a primary winding 17, as hereinafter described.

The primary winding 17 is a single conductor which is spirally wound to define a generally frusto-conical configuration having an inner turn with a diameter essentially corresponding to the inner diameter of the secondary winding 7 and an outer turn with a diameter essentially corresponding to the outer diameter of the secondary winding 7. The primary winding 17 is embedded within the plastic body 1 to the one side of the secondary winding 7 with the inner convolutions or turn aligned with the inner turns of secondary winding 7 and the outer convolution or turn aligned with the outermost turns of secondary winding 7.

A supporting fiber washer 18 is disposed between the adjacent inner turns of the primary winding 17 and the secondary winding 7. The washer has an inner diameter generally corresponding to that of the locating fiber tube 11 and an outer diameter somewhat greater than the diameter of the first turn of primary winding 17. As a result, the fiber washer 18 rests on the coplanar ends of the fiber tubes 10 and 11 and the adjacent portion of the secondary windin g 7.

The secondary to primary connecting lead 16 as most clearly shown in FIG. 3 extends from the inner end of the secondary winding 7 about the inner periphery of the fiber washer 18 and is soldered or otherwise secured to the innermost convolution of the primary winding as at 19.

The illustrated positioning of the primary winding 17 as clearly shown in FIG. 2 provides increasing insulation 20 between the convolutions or turns of the primary winding 17 and the secondary winding 7 from the inner low voltage turns to the outer high voltage turns. The insulation is therefore a minimum at the low voltage connection and maximum at the high voltage connection with a progressive increase from the former to the latter such that it is graduated generally in accordance with the voltage gradient between the windings. This provides minimum leakage inductance consistent with the provision of adequate insulation therebetween.

FIG. 3 shows a preferred system of forming the transformer or induction unit shown in FIGS. l-4. Generally,

the transformer or induction unit shown in FIGS. 14.-

Generally, the transformer is potted within a first mold 21 and a mating second mold 22. The first mold includes a central cavity 23 having a generally rectangular construction conforming to the outer configuration of the body 1 and including corner projections 24 to define the notches 6. A center post 25 is inserted into a centrally located recess in the base of the cavity 23 and extends outwardly of the cavity to a distance somewhat in excess of the depth of the body 1. A cavity 26 is provided to form one half of the socket 4. A small cavity extension 27 is provided adjacent cavity 26 to support a pin 28 which forms the opening to socket 4.

The second mold 22 is essentially the same as the first mold and includes a cavity 29 complementing cavity 23 to define a molding cavity corresponding to the shape of the body 1. The cavity 29 also includes a similar centrally located recess adapted to accommodate and receive the outer end of center post 25 with the second mold secured in abutting relation to the closing face of the first mold 21, as shown in phantom in FIG. 3. The second mold also includes a stepped cavity 30 conforming to the socket cavities 26 and 27 of the mold 21 to complete the socket 4. The second mold 22 further includes a pair of radially aligned and radially spaced primary lead openings 31.

Each of the molds 21 and 22 includes similar edge openings 32 which in the assembled relation define an input opening for introducing the plastic for forming of body 1.

In assembly, the primary winding 17 and the secondary winding 7 are separately prewound. The primary winding 17, as most clearly shown by comparison of FIGS. 2 and 5, is wound with the convolutions expanded substantially in excess of that in the assembled or the completed transformer. The secondary winding 17 is mounted on the locating and supporting tube 1 and the primary ground lead 16 is connected to the winding 17 with the washer 18 interposed between the primary and the secondary. The assembled secondary and primary windings are mounted over the center post 25 with the fiber tube 11 projecting downwardly and resting on the base of the lower mold 21. This properly spaces the secondary winding and supports the assembly within the mold 21. Core 28 is inserted into the lead jacket member 14 and has an outer stepped portion conforming to the smaller cavity extension opening 27. The second mold 22 is assembled over the primary with the leads 3 projecting through the lead openings 31. The second mold 22 is clamped in sealing engagement with the first mold 21 to form a sealed cavity into which the suitable potting compound is inserted through opening 32 in any suitable well known means. The cavity is filled with the potting compound and after it is set through any suitable means as by heat, a self-catalyst or the like, the molds 21 and 22 are separated and the completed transformer unit shown in FIG. l is removed.

The compression of the primary winding 17 positively holds itself and the secondary winding within the mold structure in properly spaced relation. This has been found to provide a very practical and reliable means for properly locating the primary and secondary windings during the molding step while producing the desired distribution of the insulating material between the secondary winding and the primary winding convolutions.

Various modes of carrying out the invention are contemplated as being within the scope of the following claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention.

I claim:

1. A transformer comprising a primary winding including a plurality of turns wound about an axis in a generally frustoconical shape to define a central opening, a secondary winding having a plurality of interconnected coil turns which are wound axially and radially about a central opening and each of which turn is axially displaced of the winding to form an annular winding having a substantially greater number of turns than said primary winding, support means mounting said primary winding coaxially of the secondary winding and to one side of the annular winding to define an unobstructed core opening.

2. The transformer of claim 1 wherein the innermost turn of said primary winding is essentially aligned with the innermost turn of the secondary winding and with the primary coil extending axially outwardly of the annular winding with the outermost turn essentially aligned with the outermost turn of the annular winding.

3. A transformer comprising a primary winding including a plurality of turns wound about an axis in a generally frustoconical shape to define a central opening, a secondary winding having a plurality of interconnected coil turns which are wound axially and radially about a central opening corresponding to the central opening of the primary winding and each of which turn is axially displaced of the winding to form an annular winding having a substantially greater number of. turns than said primary winding, support means mounting said primary winding coaxially of the secondary winding and to one side of the annular winding with said central openings aligned to define an unobstructed core opening, the innermost turn of said primary winding being essentially aligned with the innermost turn of the secondary winding and with the primary coil extending axially outwardly of the annular winding with the outermost turn essentially aligned with the outermost turn of the annular winding.

4. The transformer of claim 3 wherein said primary winding is formed of a single solid conductor.

5. The transformer of claim 3 wherein said support means includes an insulating and supporting plastic encasing both of said windings.

6. The transformer of claim 3 wherein said innermost turn of the primary winding is connected to an inner turn of said annular secondary winding.

References Cited UNITED STATES PATENTS 1,727,932 9/1929 Medved 336-231 XR 1,932,640 10/1933 Rust 336206 XR 2,445,169 7/1948 Frey 33696 XR 2,470,307 5/1949 Guanella 336231 XR 2,999,978 9/1961 Pinkley 336-23l XR 3,240,848 3/1966 Burke et a1 336-96 XR FOREIGN PATENTS 329,526 6/ 1958 Switzerland.

LEWIS H. MYERS, Primary Examiner. T. I. KOZMA, Assistant Examiner.

U.S. Cl. X.R. 

